GB2201557A

GB2201557A - Control for a heating means

Info

Publication number: GB2201557A
Application number: GB08703332A
Authority: GB
Inventors: David Stanley Purcell
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-02-13
Filing date: 1987-02-13
Publication date: 1988-09-01
Anticipated expiration: 2007-02-13
Also published as: GB2201557B; GB8703332D0

Abstract

A control for a heating means, particularly a domestic immersion type water heater 10, comprises a thermostatic switch 11 which interrupts a power supply to heater 10 when a predetermined temperature is sensed, and a latched switch R1 which when closed connects power supply 16 to switch 11, the latched switch R1 being maintained closed by a feed back signal 15 derived from supply 16 by a connection 13 between switch 11 and heater 10 so that once switch 11 deactivates the heater, the heater will remain off regardless of the thermostatic switch 11. Heater 10 may be turned on again by momentary closure of a switch 21, or when a timer 40 causes a monostable 41 to generate a turn on pulse, so that a signal passes via a diode D3 to the coil of a relay R1 having normally open contacts between supply 16 and switch 11. Closure of these contacts energises heater 10 and provides the latching signal to the relay coil via leads 15, 26, 28. A manual override switch 22 allows heater 10 to be cycled on and off by switch 11. Overheating causes a thermal fuse 31 to go open circuit resulting in opening of the contacts of relay R1 and energisation of an alarm sounding circuit 32, 34. <IMAGE>

Description

"Control for a heating means" Description of Invention This invention relates to a control for a heating means and more particularly, but not exclusively, to a domestic immersion water heater.

Conventionally, immersion heaters are controlled with simpre thermo- static switches, possibly in conjunction with a timing device. When manually switched on, or automatically switched on at a preset time by the timing means, the immersion heating element is energised and heats the water in which it is immersed to a temperature determined by the thermostatic switch. When this temperature is reached, the thermostatic switch then deactivates the element until the temperature of the water falls to a further temperature determined by the thermostat, for example, if the hot water is drawn off.

At this lower temperature, the thermostat re-energises the immersion heating element, and so on.

If only a limited amount of hot water is required, power may be wasted between when the water is drawn off which will cause the thermostatic switch to re-energise the immersion heating element, until when the immersion heating element is switched off.

It is an object of the present invention to provide a new or improved control for a heating means.

According to the invention I provide a control for a heating means, the control comprising a thermostatic switch which interrupts a power supply to the heating means when a predetermined temperature is sensed, and a latched switch, which when in an 'on' condition connects the power supply to the thermostatic switch, the latched switch being maintained in an 'on' condition by a feed back signal derived from the power supply between the thermostatic switch and the heating means.

Thus where the invention is applied to an immersion heater, once the thermostatic switch deactivates the power supply to the immersion heater element, the element will remain switched off irrespective of whether the thermostatic switch senses a temperature below that which ordinarily would cause the thermostatic switch to re-energise the immersion heater element.

It has been found that this arrangement results in a considerable energy saving.

Of course the invention may be applied to any type of heating means such as an electrically controlled gas, oil, or other water or other. liquid heater, or even to a space heating system if required.

Provided that the vessel in which the water/liquid is heated, is adequately insulated, the vessel will retain its heat for a considerable period of time after the heating meons has been deactivated by the control of the invention.

In a preferred embodiment however, the control has a manual override to enable the heating means to operate conventionally under the control of the thermostatic switch when required. Preferably this is achieved by the manual override causing the latched switch to remain latched irrespective of whether the thermostatic switch is in an 'on' condition.

The latched switch may comprise an electromechanical relay', the coil of which is energised by the feed back signal once the heating means has been energised. Alternatively, a solid state switching device may be used provided that the switching device can handle the current the heating means consumes.

The control may include a temperature sensitive circuit breaker, such as a thermal fuse which under normal conditions presents a short circuit across its terminals, but senses a temperature above a predetermined temperature and presents an open circuit across its terminals in response, to cause the latched switch to be switched to an 'off' condition.

The circuit breaker may be positioned to sense any overheating caused by the heating means for example due to a faulty thermostatic switch, or a lack of substance, i.e. water or other liquid or air, being heated.

The control may include an alarm circuit which sounds an alarm at least for a short period of time such as several seconds, should the temperature circuit breaker present an open circuit across its terminals. Thus a user of the system is warned that the circuit breaker has sensed an excess temperature and that maintenance and/or repair work is necessary.

Preferably, the circuit breaker is a fuse which is non user serviceable but needs to be replaced once the fuse has sensed an excess temperature.

However if required, the fuse may be of the type which can be reset although this may not be desirable as this could lead to a user of the control overriding the safety feature.

The control may further comprise a timer circuit to enable the control to be used in conjunction with a conventional timer.

The timer may, at a preset time, deliver a signal to the timer circuit which thus causes the latched switch to be switched to an 'on' cition to energise the heating means. Preferably, the timer circuit then isolates the timer from the latched switch so that the heating element is switched off by the thermostatic switch when a predetermined temperature has been obtained, and remains switched off regardless of whether the timer is providing a signal to the timer circuit.

Preferably the latched switch, the alarm circuit where provided, and the timer circuit where provided, operate at a voltage lower than the voltage which is applied to the heating means.

The control may include a control panel including at least two switches to enable a user to select conventional operation of the heating means, or control of the heating means in accordance with the invention, by selecting the necessary switch.The control panel may also include an 'on/off' switch to isolate the feedback signal from the latched switch.

Preferably the switch which selects control of the heating means in accordance with the invention comprises a temporary switch which enables current to pass only when manually pressed, to cause the latched switch to latch, but when released, preventing further current from passing. It will be appreciated that the feed back signal will maintain the latched switch in an 'on' condition.

The invention may particularly be applied to the control of a domestic immersion type water heater.

The invention will now be described with the aid of the accompanying drawing which is a diagrammatic view of a circuit for a control in accordance with the invention.

Referring to the drawing, a heating means comprises an immersion type electrical heating element 10, which is mounted so as to provide heat directly to water in a vessel in which the element 10 is mounted.

The heating element 10 is connected electrically in series with a conventional thermostatic switch II which senses the temperature of the water being heated, the terminals for the heating element 10 and the thermostatic switch II being contained within a housing 12. One terminal, marked 13, of the thermostat and one terminal, marked 14, of the heating element 10, are connected together directly, and to a feed bock connection 15, the purpose of which will become apparent hereinafter.

p The thermostatic switch I i is part of a control which includes a latched switch, in this example an electromechanical relay RI. Of course in a suitably modified circuit, a solid state switch which operates in the manner of a relay could instead be provided. The contacts of the relay RI are normally open, but are closed when a coil of the relay RI is energised by an adequate current. When the contacts of the relay RI are closed (as shown) current may pass from a supply 16 which is in this case a mains 240 volt 50 cycles supply, to the free terminal 17 of the thermostatic switch I I.

When the thermostatic switch 11 is also closed (as shown) current may thus pass through the heating element 10 to a terminal 18 which is connected to neutral. Thus the heating element 10 may effect direct heating of the water in which the heating element 10 is immersed.

The contacts of the relay RI are closed when the necessary controls of a control panel 20 are operated.

The control panel 20 comprises a push to make, sprung push button switch 21, which, when the button is pressed completes a circuit through the switch 21 and when released, the circuit through the switch is broken.

In parallel with the switch 21 there is a manual override switch 22 which when closed remains closed until manually opened.

The switches 21 and 22 may if desired, be incorporated into a common switch housing and may alternatively be operated by a common switch member.

When the push button switch 21 is closed, current may pass from the mains supply 16 to an output terminal 24 of the control panel 20, via the contacts of an on-off switch 25. This output from terminal 24 is connected via a conductor 28 to a latching circuit which is described below, where this establishes or maintains the current supply to the coil of relay RI to close, or maintain closed, the contacts of the relay Rl.

Thus power is supplied through the thermostatic switch II to the heating element 10.

When the push button switch 21 is released, current supply to the heating element will automatically be maintained. This is achieved because the feed back connector 15 is connected via a relay R2 whose contacts are normally closed, to another conductor 26 to a point 27 downstream of the push button switch 21 and manual switch 22, but upstream of the on/off switch 25 and hence to terminal 24. Thus once current is passing through the element 10, a current supply to the coil of relay RI and hence to the heating element 10 will be maintained, at least until the thermostatic switch tt- opens.When this occurs, the current supply fed via the feed back connector IS and relay R2 and conductors 26 and 28 to the coil of relay Ri will be interrupted and thus the contacts of relay RI will open and remain open until either switch 21 is again activated, or until switch 22 is switched on, or until a timer provides the necessary trigger signal to cause relay R I to latch on.

This operation is described below.

When switch 22 is switched on, not only is a signal provided to terminal 24, but also a coil of relay R2 will be energised. The side of coil R2 remote from the switch 22 is connected to a neutral terminal 18'. The purpose of relay R2 is to isolate the feed back connector 15 from the conductor 26 when manual override switch 22 is operated.

An indicator lamp LI such as a neon lamp built into switch-22 will also be energised when switch 22 is activated, lamp L2 also being connected to a neutral terminal 27' which may be connected to terminals 18 and 18'.

A further lamp L2, also possibly a neon lamp will be lit whenever an output is provided to terminal 24 of the control panel 20, either via push button switch 21, manual switch 22, or the feed back circuit, lamp LI also being connected to the neutral terminal 27'.

Operation of the latching circuit will now be described.

The feed back signal from terminal 24 will be virtually at mains voltage and is connected to one end of a coil which provides one side of a stepped down transformer TI, via conductor 28, the other end of the coil being connected to a neutral point 45. The opposite side of the transformer Tl includes a rectifying circuit having a pair of diodes DI and D2 and a centre terminal of the coil is connected to a zero voltage rail 30. The reduced voltage rectified feed back signal is then fed via an isolating diode D3 to one end of the coil of relay Rl. The other end of the coil is connected to rail 30 via a temperature fuse 31, the operation of which will be described later.

The latching circuit also includes a large storage capacitor C I which both smooths the reduced signal and stores a charge for powering an alarm.

A diode D4 is also provided in parallel with the coil of relay RI to protect other components of the circuit from currents induced in the coil of the relay dbe to back e.m.f.s..

The thermal fuse 31 usually presents a short circuit to the feed back signal passing through the coil of relay RI but is arranged upon a predetermined temperature being sensed to present an open circuit. In this event, even though current may still flow through the coil of reJay~RI by virtue of connection to earth rail 30 through an alarm circuit 32, which is described later, this current is insufficient to maintain the contacts of relay RI closed so that relay RI opens thus interrupting the power supply to the heating element 10.

Thermal fuse 31 is preferably positioned on an outlet or expansion pipe from the vessel in which the water being heated is contained, and may be connected to earth as shown, via the pipework of the system. The fuse 31 senses overheating due to, for example, insufficient water being present in the vessel, or a faulty thermostatic switch 11 or the like.

The fuse 31 may be arranged to present an open circuit at 840C for example and to remain open until reset or replaced after any necessary maintenance or repair work to the heating element 10, the switch II, or associated control, or to the water system, has been effected.

If the switch 22 is open, when the fuse 31 goes open circuit, the capacitor CI will discharge through the alarm circuit 32 even though the feed back signal will no longer be provided.

The alarm circuit 32 comprises an integrated circuit ICI of the '555' type. A high pitch buzzer 34, a pair of resistors 35,36, and a capacitor C2 arranged as an oscillator so that the discharging capacitor Cl causes the buzzer 34 to sound for a short period until the capacitor C I is discharged below a level acceptable to the alarm circuit 32.

If switch 22 is closed when the thermal fuse 31 presents an open circuit, the feed back signal to the alarm circuit 32 will be maintained even though the current passing through the coil of relay RI will be insufficient to maintain the contacts of the relay closed. Thus the alarm circuit 32 will continue to sound the alarm buzzer 34 until either the on-off switch 25 of the control panel 20 is operated, or until the circuit through fuse 31 is restored.

Preferably, the fuse 31 is of the non user serviceable type although if desired, may be of the type which can be reset. Alternatively, any other type of temperature sensitive circuit breaker may be provided.

The purpose of the thermal fuse 31 or other temperature sensitive circuit breaker is to protect the heating system from overheating.

The invention may be used in conjunction with a conventional timer 40 so that the heating element 10 may be switched on at a predetermined time, the timer providing a current through a timer circuit 41 for a brief period of time sufficient to cause the relay RI to latch on in the same manner as if switch 21 of the control panel 20 had been activated by a user.

The timer 40 is connected to one side of a coil of a second stgp down transformer T2, the other side of the coil being connected to neutral point 45. The other side of the transformer T2 has a rectifier comprising a pair of diodes D5,D6 and a smoothing capacitor C3. Thus the high, usually mains, signal produced by the timer 40 is reduced and rectified.

The reduced and rectified signal is fed to an integrated circuit IC2 which again is a '555' type. The integrated circuit IC2 is arranged in a circuit of resistors 42,43, and capacitors C4,CS as a monostable circuit, and an output is produced which passes along line 44 which is connected via diode D3 to the coil of relay RI.

When the integrated circuit IC2 receives a signal from the timer 40 at a preset time, to switch on the heating element 10, the output alo g jline 44 is provided only for a limited period of time or until the monostabie circuit 'flips' to an off condition. However once the coil of relay R I is energised, the relay RI will be latched'on' as hereinbefore described by virtue of the feed back connection 15, and the conductors 26 and 28, until the thermostatic switch II senses a predetermined temperature at which point the heating element 10 will be switched off and remain switched off even when hot water is drawn off, and regardless of whether any signal is still being provided from the timer 40 to the timer circuit 41.

Thus in effect, the timer circuit 41 isolates the timer 40 from the latched switch RI once the heating element 10 is switched on, and the circuits hereinbefore described take over the control of the heating element 10.

Various modificotions may be made without departing from the scope of the invention.

For example, the latching circuit, the fuse 31 and alarm circuit 32, and the timer circuit 41 are only given as examples and it will be apparent to those skilled in the art that alternative circuits could be devised to achieve the functions of these circuits. For example, the circuits could be replaced by a suitable logic controller.

Although the invention has been described with reference to controlling a heating element of an immersion type water heater, the invention may be applied to any other electrically controlled heating means such as an oil or gas water heater, or even a space heater, Thus the substance being heated by the element 10 need not be contained in a vessel and the heating element 10 need not be immersed in the substance being heated.

The control described enables a heating means to be operated conventionally, but also enables a considerable saving in fuel should a user forget to switch off the heating means once the substance being heated has reached a predetermined temperature. Further, a control provides a safety feature in the event of for example, an immersion heating element 10 being provided with power when insufficient water is present in the vessel, which in the absence of the fuse 31 and alarm circuit 32, could lead to serious damage or even danger.

The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, or a class or group of substances or compositions, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

I. A control for a heating means, comprising a thermostatic switch which interrupts a power supply to the heating means when a predetermined temperature is sensed, and a latched switch, which when in an "on" condition connects the power supply to the thermostatic switch, the latched switch being maintained in an "on" condition by a feed back signal derived from the power supply between the thermostatic switch and the heating means.
2. A control according to claim I which has a manual override to enable the heating means to operate conventionally under the control of the thermostatic switch when required.
3. A control according to claim 2 wherein the manual override when operated causes the latched switch to remain latched irrespective of whether the thermostatic switch is in an "on" condition.
4. A control according to any one of claims I to 3 in which the latched switch comprises an electromechanical relay, a coil of which is energised by the feed back signal once the heating means has been energised.
5. A control according to any one of claims I to 4 wherein the control includes a temperature sensitive circuit breaker which under normal conditions presents a short circuit across its terminals, but senses a temperature above the predetermined temperature and presents an open circuit across its terminals in response, to cause the latched switch to be switched to an "off" condition.
6. A control according to claim 5 wherein the circuit breaker is positioned to sense any overheating caused by the heating means.
7. A control according to claim 5 or claim 6 which includes an alarm circuit which sounds an alarm at least for a short period of time should the temperature circuit breaker present an open circuit acorss its terminals.
8. A control according to any one of claims 5 to 6 wherein the circuit breaker is a fuse which is non user serviceable and needs to be replaced once the fuse has sensed an excess temperature.
9. A control according to any one of claims 5 to 7 wherein the circuit breaker is a fuse of the type which can be reset.
10. A control according to any one of the preceding claims which comprises a timer circuit to enable the control to be used in conjunction with a conventional timer.
I I. A control according to claim 10 wherein the timer may, at a preset time, be arranged to deliver a signal to the timer circuit which thus causes the latched switch to be an "on" condition to energise the heating means, and then isolates the timer from the latched switch so that the heating element is switched off by the thermostatic switch when the predetermined temperature has been obtained, and remains switched off regardless of whether the timer is providing a signal to the timer circuit.
12. A control according to any one of the preceding claims wherein the latched switch, the alarm circuit where provided, and the timer circuit where provided, operate at a voltage lower than the voltage which is applied to the heating means.
13. A control according to any one of claims 2 to 12 where appendant to claim 2 wherein the control includes a control panel including at least two switches to enable a user to select conventional operation of the heating means, or control of the heating means in accordance with the invention, by selecting the necessary switch.
14. A control according to claim 13 wherein the control panel also includes an "on/off" switch to isolate the feedback signal from the latched switch.
15. A control according to claim 13 or claim 14 wherein the switch which selects control of the heating means in accordance with the invention comprises a temporary switch which enables current to pass only when manually pressed, to cause the latched switch to latch, but when released, prevents further current from passing.
16. A control substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
17. In combination, a contrpl according to any one of the preceding claims and a domestic immersion type water heater.
18. A combination according to claim 17 substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
19. Any novel feature or novel combination of features as disclosed herein and/or as shown in the accompanying drawings.